Earlier quoted context omitted.
An encrypted hdd/ssd will help of someone steals your computer, removes your drive, and tries to read it from another computer in order to bypass your passwords. It won’t do shit for ransom ware. Ransom ware runs as a user land program and does encryption from within your OS where you data is live and unencrypted. The end result will be a hard drive full of encrypted files that is then reencrypted by bitlocker.
If someone steals your computer, they also have the TPM, which has the key, right? What am I missing about what TPM does that is so secure?
I would guess extracting the keys from the tpm in other ways is not impossible, but probably sufficiently hard to be not worth it in most situations.